The stability of cementite formed during the reduction of hematite and preoxidized titanomagnetite ores in a methane-hydrogen gas mixture was examined in the temperature interval 500oC to 900oC for the hematite ore and 300oC to 1100oC for titanomagnetite. Cementite formed from hematite ore was most stable at temperatures between 750oC to 770oC. Its decomposition rate increased with decreasing temperature between 750oC and 600oC and with increasing temperature above 770oC. Cementite formed from preoxidized titanomagnetite was most stable in the temperature range 700oC to 900oC. The rate of cementite decomposition increased with decreasing temperature between 700oC and 400oC and with increasing temperature above 900oC. Cementite formed from titanomagnetite ore was more stable than cementite formed from hematite under all conditions examined.